enable PIE for dynamically linked Linux host executables

Compile all host programs for Android with -fPIE and -pie. This
enables PIE (Position Independent Executables), which helps
protect these applications from exploitation due to memory
management bugs.

Note: PIE *static* executables are not supported at this time. darwin
and windows are also not supported.

Change-Id: I67c1be297711ea23064c349f97ebd02eef3eff09
Merge "enable PIE for dynamically linked Linux host executables"
Merge branch 'master' of https://android.googlesource.com/platform/build into HEAD